Device for dry separation of precious metals from finely divided material



June 6, 1939. 'L'HEJBIGELOW DEVICE FOR DRY SEPARATION OF PRECIOUS METALS FROM FINELY DIJIDED MATERIAL Filed Sept. 7, 1935 INVENTOR.

9 ATTORNEY I REISSUED Patented June 6, 1939 DEVICE FOR DRY SEPARATION oF PREoIoUs" METALS FRoM FINELY DIVIDED MATE- RIAL Leroy E. Bigelow, Glendale, Calif.

Application September 7, 1935, Serial No. 39,595

4 Claims. (Cl. 209-431) My invention relates to a device for the dry sepwardly in the chute l2 into the receptacle ID. A aration of precious metals such as gold, silver, gravity closing inlet valve I4 is preferably proplatinum and the like from finely divided mavided which remains open as long as material is terial. Without limiting this invention and setpassing downwardly from the hopper. ll intothe 5 ting the following forth merely as one example, receptacle Ill. The gravity closing inlet valve l4 5 I have found that my invention is well suited comprises a valve member i5 supported by pivot for thedry separation of finely divided precious I6 and provided with a longitudinally adjustable metals, such as gold, from finely divided dry counterweight means IT. The counterweight material, such as desert sand. I means I! is longitudinally adjusted on the lever 10 It is an object of my invention to provide a l8, so that any appreciable weight of materials 10 machine which will separate and remove by present on the gate IE will maintain the gravity gravity the heavier particles of precious metals, closing valve means 14 in open position. In the,

as gold from finely divided material. absence of material on the gate 15, the weight It is a further object of my invention to prol'l moves the valve means M into closed position. i; vide mechanism which will permit the lighter At the other end and on the bottom of the particles of precious metals,such as flour gold, to receptacle [0 is an outlet valve means I9. This be suspended in air and electrostatically removed outlet valve means I 9 is also preferably a gravity from such suspension. closing valve and is provided with a gate It is another object of my invention to proconnected with an arm or shaft 2| and a counter- 0 vide a device employing an air flotation process weight 22 which is longitudinally adjustable on 20 having a plurality of chambers, each of which the shaft 2|. The counterweight 22 may be adhas separately controlled air pressure, permitjusted longitudinally of the shaft 2| so that the ting adjustment of the rate of flow of materials outlet valve 19 will be maintained open with the through the separating device. presence of a predetermined amount of material It is another object of my invention to proon the gate 20. A substantially horizontal screen vide electrostatically charged plates of a parsection 23 is provided adjacent the outlet end ticular shape, which will aid in the separation of portion of the machine and a substantially inthe relatively light precious metals from the clined screen section 24 is pro'vided'substantially finely divided material. adjacent the inlet end portion of the machine.

The above mentioned general objects of my A plurality of chambers, such as chambers 25, 30 invention, together with others inherent in the 26 and 21, are provided below the screen section same, are attained by the mechanism illustrated 23. Another plurality of chambers, such as in the following drawing, the same being prechambers 28 and 29, are provided below the inferred exemplary forms of embodiment of my clined screen section 24. An air reservoir 3!] is invention, throughout which drawing like referconnected to a source of air pressure, as a blower ence numerals indicate like parts: 3i, which is driven by any suitable source of Figure 1 is a vertical sectional View of a depower, such as electric motor 32 and belt means vice embodying my invention; 33. The reservoir 30 is connected by separate Fig. 2 is a detached fragmentary plan view of conduits 34, each of which is provided with a a tray and a plurality of electrostatically charged separately adjustable valve means 35, with the 40 plate members; chambers 25 to 29 inclusive. For purposes here- Fig. 3 is a detached fragmentary sectional View inafter discussed, by the adjustment of a valve on a larger scale of parts of the air blastmeans; 35, any desired pressure may be created in the Fig. 4 is a detached fragmentary plan view of chambers 25 to 29, inclusive. The screen secparts of the air blast means; tions 23 and 24, which form the upper surface 45 Fi 5 is a fragmentary Sectional w O a of the chambers 25 to 29, inclusive, are of a suifimodified form of trough means positioned below ciently fine mesh to prevent the passage of mathe electrostatically charged plates; and terial downwardly therethrough into the cham- 6 s a d a ed fragmentary sectional view bers 25 to 29 inclusive. In providing such screen of a modified form of electrostatically charged for relatively fine material, I have taken a 500 50 plate. mesh screen of approximately inch thickness In the drawing a substantially closed receptacle and rolled said screen to provide smaller Open- I0 is connected at one end with a hopper II and ings in the screen. After the screen was rolled, a gate valve I2 may be opened and closed to perit is believed that the openings in such a screen mit the material in the hopper ll to pass downwere of a size approximately equal to the openings in a 750 mesh screen. For coarser material, a coarser screen may be used. The purpose of providing relatively fine openings in the screen sections 23 and 24 is to prevent material passing downwardly therethrough and at the same time to provide openings which will permit the desired air pressure in the chambers 25 to 29 to be maintained. I have found in operation that pressures ranging up to twenty pounds are necessary for different types of material in the respective chambers 25 to 29, inclusive.

The relatively light precious metal, such as flour gold, suspended in the finely divided material above the screen section 23, is raised by air pressure so as to be separated by means of the electrostatically charged plates 38 and 31, which are above the screen section 23.

The end wall 38 of the receptacle I8 is preferably inclined at an angle of substantially 45. The lower end of the inclined wall 38 is in spaced relation to the lower end of the inclined screen section 24 providing between said members a discharge outlet chamber 44 for heavy particles of material. Preferably a plurality of air conduits as conduits 39 and 39 are provided in the discharge outlet chamber 44. The air conduit 39 is preferably positioned near the lower end of the chamber 44 and the air conduit 39' is preferably positioned adjacent the upper opening of the chamber 44. Conduit means 48 connects the air conduits 39 and 39 with the air reservoir 38. A valve 48' is provided in conduit 48 for adjusting the air pressure to the conduits 39 and 39. The air conduit 39 is preferably provided with downwardly and horizontally directed openings 4!. The air conduit 39 is preferably provided with angularly positionedopenings 42 which are directed downwardly and outwardly.

In Fig. 4 I have shown a fragmentary plan view of the conduit 39 and the means connecting the same to the conduit 4. Stuifing box 52 and nuts 53 of standard construction are employed, permitting conduit 39 to be angularly adjusted as desired, and the air tight connection between the conduits 39 and 48 maintained.

An angularly disposed bafile plate 43 is preferably provided above the air conduit 39'.

A chamber 61 is provided adjacent the end wall 38 in communication with the interior of the machine. A screen 58 forms a continuation of the wall 38 and extends over the opening between the chamber 61 and the interior of the machine. An air pressure supply conduit 69 having a valve l8 therein is connected with the chamber 67. The conduit 89 is connected with the air reservoir 38, preferably by connecting said conduit 69 with the conduit 40 between the valve 48 and said air reservoir.

As material passes from the hopper H past the inlet valve and downwardly along the wall 38, it is affected by the air which is being discharged through the openings 4i of the conduit 39; the openings 42 of the conduit 39, and the screen 88. The finely divided material containing the precious metals is agitated by this air. The relatively heavier particles move downward- 1y by gravity along the wall 38 and into the chamberr 44. Rotatable rubber rolls 45 serve to provide an air seal at the bottom of the chamber 44. These rolls are preferably driven at relatively slow speeds from a source of power, as electric motor 32, by means of a belt 45, a clutch mechanism 41, a speed reduction means 48 and a belt 49. The drive means and clutch mechanism, for independently controlling the operation of the rolls 45, is only somewhat diagrammatically indicated. However, as this may be done by many well known means, it is believed that such diagrammatic indication is sufficient. The air from the conduit 39 and 39 tends to keep the finely divided material in the chamber 44 in a state of agitation permitting the heavier particles to move downwardly to the bottom of the chamber. The heavier particles pass downwardly between the rubber rolls 45 into the receptacle 58. The finer particles of metal and the finely divided materials pass upwardly to maintain the level which is indicated at 5!. As the material rises, due to the action of the air from the conduits 39 and 39 and chamber 87, it passes in the direction of the arrow between the wall 38 and the bafile plate 43. In view of the fact that the screen section 24 and the wall 38 are inclined towards each other to form a substantially V shaped hopper, a relatively large body of material must be maintained in agitation over said members, as compared to the amount of material which remains in agitation over the screen member 23. The air passing through conduits 39 and 39, to gether with the air passing through the screen sections 24 and 88, is sufiicient to maintain the material in agitation above said screen section 24 and said wall 38.

The particles of metals which are of a size smaller than the size of particles which have been separated out, and which ran down the wall 38 into the chamber 44, move with the material in the substantially V shaped hopper in a substantially rotary direction. These particles are deposited on the screen section 24 and graduate in size, the heavier being deposited on the screen section directly above the chamber 29, while the lighter are deposited on the screen section 24 above the chamber 28. Also due to the agitation of the material directly above the screen section 24, these-particles are separated out by gravity and work down the screen section 24 into the chamber 44 and thence are delivered through the rolls 45 into the chamber 50.

Electrostatically charged plates are also used to complete the separation of the metallic substances from the finely divided material. The electrostatically charged plates 36 and 3'7, which are positioned above the screen section 23, and which are shown in plan in Fig. 2, together with the electrostatically charged plates 54 and 55, which are present in chamber 28, are spaced apart from approximately A9, to 2" depending upon the class of material in the machine. The plates 36 and 54 are the positive plates, while the plates 31 and 55 are the negative plates. It is desirable that as high a voltage of direct current be impressed on these plates as may be done without the electrical energy arcing from one plate to the other. In view of the fact that such information is well known in the electrical art, I will not set forth complete data relative spacing and strength of voltage. However, I prefer to use a voltage of at least 2,000 voltsthe exact voltage depending upon the spacing between the plates. For convenience, alternating current may be rectified by well known means, and the resulting pulsating current of the desired voltage, having a relatively low amperage, is very satisfactory and suitable for impressing a voltage on the said plates. As relatively high voltage electrical energy is discharged between the plates 55 and 54 (without arcing, as above indicated), the positive plates 54 tend to electrostatically attract non-magnetic, as well as magnetic metals towards said positive plates. This force attracting the non-magnetic precious metals towards the plates 54 tends to maintain the same against the inclined screen section 24. In view of the fact that the openings in the screen aresmall, relativelyfine particles of precious metals cannot pass therethrough. The presence of the electrostatically charged plates 53 at this position serves as means to prevent the precious metals of a size larger than fiour gold from movingwith the finely divided materials toward the discharge end of the machine.

Thus far, the heavier and relatively lighter particles of metals have been separated out of the mass of finely divided material. In some desertsand, a great amount of values in the form of flour gold are found.- A certain amount of these values will be in the finely divided materialas it passes over the screen section 23. As such values pass over this screen section 23 the air passing upwardly through said screen will carry the said values upwardly into the field of the plates 35 and 3'1. Also the air which raised the particles of such finely divided previous metal adjacent the bafile 43, raised this finely divided metal or flour gold into the field of the plates 36 and 37. The plates 33, being positively charged, will electrostatically attract the flour gold to said plates. Preferably the plates 35 are coated with mercury, and the flour gold will amalgamate with said mercury and the flour gold can be recovered from said amalgamation by any well known means.

Also preferably trough like members 56 are supported below the plates 23. In Fig. 5 of the drawing I have shown an alternative shape of trough which is numbered 57. In Fig. 6, I have shown an alternative form of plate which may be substituted for the plate 35. This plate shown in Fig. 6 is provided with integral inclined sections 53 and 59 formed by punching out sections of the metal of the plate in alternate directions, leaving openings 60. Material, passing from an upper portion toward a lower portion of the plate shown in Fig. 6, will be directed by the inclined sections 58 and 59 and may pass alternately from one side of said plate to the other and ultimately from the lower edge of said plate into the trough like member 56. This particularly shaped plate seems to aid in retaining the flour gold on the plates.

A source of electrical energy for charging the plates 54, 55, 36 and 31 is indicated by means of conductors 6| and 32 connected to a source of energy (not shown). The conductors 6| connect the positive plates to such a source of electrical energy, and the conductors B2 connect the negative plates to such a source of electrical energy.

For convenience in operation, preferably a door 33 is provided so that the values recovered in the chamber 55 may be conveniently removed. To obtain the values which are recovered by the plates 36, it is preferable that the plates be of such construction that they may be readily removed from the machine. This may be done by mounting the plates 36 and 31 in trays 65, which trays are slidable into and out of the machine. The plates 36 and 31 preferably slide vertically into slots 56, which are provided at spaced intervals in the sides of the trays, whereby plates may be readily removed from the trays individually.

After the plates are removed from the machine, the values, which are in the troughs 56, may be readily recovered and the values which have collected on the plates 56 may be removed by scraping the plates. In the event that mercury has been used, the amalgam containing such values may be scraped from the plates. The concentrates thus recovered from the plates 36, the

troughs 56 and from the chamber 50 may be further refined by well known apparatus.

In the operation of the apparatus described, the finely divided material, which may be as above indicated, desert sand or artificially produced finely divided material, is placed in the hopper I I and permitted to discharge from said hopper past the gate valve l2 and past the gravity closing intake valve I 4. When such finely divided material enters the relatively closed receptacle l0, it is agitated by the air until the same substantially assumes the level indicated at 5|. As the supply of material is increased, the gravity closing discharge means will open, due to the presence of material thereon, and as the agitated mass of finely divided material attempts to seek its own level, it discharges from the gravity actuated discharge valve means l9, and out the chute 64. To increase the rate of discharge of the material it is only necessary to adjust an individual valve means 35 of a. chamber 25, 26 or 21. As the pressure in said chambers is increased, the rate of discharge of the material is thereby accelerated. The pressure necessary in the respective chambers depends upon the rate of separation. Should it be found that any values are present in the material as it leaves the discharge chute 54, the individual valves 35 should be adjusted to decrease the rate of fiow of material through the receptacle. By providing individual valve control means for each of the receptacles, I provide a means for readily adjusting the rate of fiow of the material through the receptacle, which rate should be determined to be the maximum rate of flow possible with a maximum recovery of the precious metals. In the event that finely divided material, having a high percentage of relatively fine or flour gold, is being run through the machine, then the rate of How should be less to permit all of such flour gold to be recovered by the electrostatically charged plates and to thereby provide a maximum recovery of such values. Also in the event that the material is in an extremely fine state of subdivision, the pressures in the chambers 25, 26 and 21 below the screen section 23 must be decreased and the pressures in the chambers 28 and 29 and in the conduit 39 must be relatively decreased to provide sufficient agitation of the finely divided material to effect a most efiicient operation of the device.

Obviously, changes may be made in the forms, dimensions and arrangement of the parts of my invention, without departing from the principle thereof, the above setting forth only preferred forms of embodiment.

I claim:

1. A device for the dry concentration of precious metals from finely divided material, comprising a receptacle; material inlet means at one end portion of the receptacle and material outlet means at the other end portion of the receptacle; a screen like bottom of fine mesh in said receptacle supporting finely divided material and allowing the passage of air therethrough, said screen like bottom having a section upwardly inclining from the inlet end portion toward the outlet end portion, and a substantially horizontal section extending from the inclined section to- Ward the outlet end portion; air pressure supply means operatively positioned below said screen. and directing a blast of air upwardly through said screen and said material; metal plates positioned below and adjacent to said inclined screen section; and means impressing a relatively high voltage on said plates.

2. A device for l the dry concentration of precious metals from finely divided material, comprising a receptacle; material inlet means at one end portion of the receptacle andmaterial outlet means at the other end portion of the receptacle; a screen like bottom of fine mesh in said'receptacle supporting finely divided material and allowing the passage of air therethrough, said screen like bottom having a section upwardly inclining from the inlet end portion toward the outlet end portion, and a substantially horizontal section extending from the inclined section toward the outlet end portion; air pressure supply means operatively positioned below said screen and directing a blast of air upwardly through said screen and said material; discharge outlet means for heavy particles of material positioned adjacent the lower end portion of the inclined screen section; air seal means operatively positioned as respects said discharge outlet means; and means positioned within said receptacle and discharging a blast of air into said discharge outlet means, whereby material will be urged against entering said outlet means.

3. A device for the dry concentration of precious metals from finely divided material, comprising a receptacle; material inlet means at one end portion of the receptacle and material out let means at the other end portion of the receptacle; a screen like bottom of fine mesh in said receptacle supporting finely divided material and allowing the passage of air therethrough, said screen like bottom having a section upwardly inclining from the inlet end portion toward the outlet end portion, and a substantially horizontal section extending from the inclined section toward the outlet end portion; air pressure supply means operatively positioned below said screen and directing a blast of air upwardly through said screen and said material; discharge outlet means for heavy particles of material positioned adjacent the lower end portion of said inclined screen section; two driven rolls of soft rubber operatively positioned in said discharge outlet means discharging said heavy particles therefrom and maintaining a substantial air seal, and means positioned within said receptacle and discharging a blast of air into said discharge outlet means, whereby material will be urged against entering said outlet means.

4. A device for the dry concentration of precious metals from finely divided material, comprising a receptacle material outlet means at one end portion of the receptacle; material inlet means at the other end portion of said receptacle; an inclined wall below said material inlet means; a screen like bottom of fine mesh in said receptacle supporting finely divided material and allowing the passage of air therethrough, said screen like bottom having an inclined section with its lower end positioned adjacent the lower end of said inclined wall; discharge outlet means for heavy particles of material positioned adjacent the lower end of said inclined screen section and said inclined wall; means positioned within said receptacle and discharging a blast of air at the location of said discharge outlet means; and means discharging air upwardly through said screen like bottom, whereby material will be urged against entering said outlet means.

LEROY E. BIGELOW. 

